1. Field of the Invention
The present invention relates to sand blasting apparatus and the like, and, more particularly, to an aspiration-type sand blasting apparatus which utilizes an improved aspirator probe for ducting media and carrier gas from a media reservoir through a media supply conduit to the mixing chamber of a discharge nozzle, which provides for a controlled flow of liquid from a liquid reservoir through a liquid supply conduit to the mixing chamber, and which causes the media, the carrier gas and the liquid to combine with a propulsion fluid in the mixing chamber for discharge from the nozzle.
2. Prior Art
It is known to provide a portable sand blasting apparatus with a media aspirator probe which can be inserted into a reservoir of flowable blasting media, such as granular sand, for supplying a mixture of media and a carrier gas, such as air, through a supply conduit, to a discharge control nozzle. The nozzle is supplied with pressurized propulsion fluid, such as compressed air, which is caused to flow through the nozzle. The propulsion fluid travels along a flow path that extends substantially centrally through a mixing chamber defined within the nozzle. The propulsion fluid operates, as by aspiration, to draw a vacuum in the media supply conduit and in the media probe, whereby ambient air pressure causes media and a carrier gas, namely air, to move through the probe and through the media supply hose to the nozzle. The mixture of media and carrier gas is introduced into the flow of propulsion fluid. A forceful delivery of the media, the carrier gas and the propulsion fluid discharges from the nozzle in a controlled direction for treating workpiece surfaces.
As is discussed in introductory portions of the referenced Aspirator Probe Case, a previously proposed aspirator probe construction includes two parallel tubes of unequal length positioned side-by-side and welded together. The probe is oriented substantially vertically with lower ends of both tubes extending into a supply of flowable blasting media such as granular sand. One of the tubes is longer than the other, and its upper end projects upwardly beyond the upper end of the shorter tube. The lower ends of both tubes are coextensive. The longer of the tubes is a delivery tube for supplying a mixture of sand and air through a supply hose to a control nozzle. The shorter of the tubes is an air supply tube. Aligned holes are drilled through adjacent walls of the delivery and air supply tubes to provide a port which communicates both of the tubes. When the discharge control nozzle is activated, pressurized propulsion fluid passing through the nozzle creates an aspiration effect which draws a vacuum in the media supply hose and in the delivery tube of the probe. Ambient air pressure operates on sand in the container to force sand into and through the delivery tube, and through the supply hose to the control nozzle. As sand rises in the delivery tube, an additional aspiration effect operating in the probe causes air to be drawn into the delivery tube from the air supply tube through the communicating port. The air which is drawn into the delivery tube mixes with the sand to provide a sand and air mixture that is supplied to the control nozzle. The aspiration effect which operates within the probe provides a means of metering sand and air for supply to the control nozzle. Since aspiration takes place within the probe, the probe is known in the art as an aspirator probe.
A problem with the above-described aspirator probe proposal is that the operation of the probe tends to change undesirably with variations in the pressure of the propulsion fluid which is supplied to the control nozzle. A further problem lies in a pulsating, relatively uneven delivery of sand which occasionally results with use of the probe. Another problem is that, in order to drill a communicating hole through abutting walls of the side-by-side delivery and air supply tubes, it is necessary to drill an additional hole through the opposite wall of one of the tubes in order to gain access to the area where a hole can be drilled through abutting walls of the two tubes. The drilling of this additional hole adds to fabrication cost. The presence of this additional hole is also found, in some instances, to detract from proper operation or the probe.
A further problem with prior sand blast apparatus proposals is that undesirable clouds of dust may tend to be generated not only as the dry media discharges from the nozzle but also as the dry media travels through the air and impacts a surface being blasted. Some prior proposals have attempted to overcome this problem by introducing a flow of liquid into the discharging stream of media, carrier gas and propulsion fluid. A problem with prior liquid injection proposals lies in the non-uniformity of the relative percentages of media and liquid in the mixtures which discharge from the nozzles. This non-uniformity results, at least in part, from the pulsating, relatively uneven delivery of media provided by the previously described aspiration probes. Still another drawback common to most prior liquid injection proposals is their failures to provide a control for regulating the relative percentages of liquid and media in the flow which discharges from the nozzle.
3. The Referenced Applications
The invention of the referenced Aspirator Probe Case addresses the problem of providing an improved aspirator probe by providing an improved probe having a tube-within-a-tube construction that utilizes a mixture delivery tube which is surrounded along a majority of its length by an air supply tube. In preferred practice, the air supply tube has an inner diameter that is larger than the outer diameter of the delivery tube. The delivery tube is longer than the air supply tube and has an upper end which projects upwardly beyond the upper end of the air supply tube for connection to a delivery hose. The delivery tube has a lower end which is either coextensive with or recessed within the lower end of the air supply tube. A communicating formation is provided for permitting a restricted flow of air to pass from the air supply tube into the delivery tube.
One probe embodiment described in the referenced Aspirator Probe Case utilizes a communicating formation which takes the form of a non-coextensive arrangement of the lower ends of the delivery and air supply tubes. In another described embodiment, the communicating formation takes the form of a hole, slot, notch or the like, provided in a side wall portion of the delivery tube. In still another described embodiment the communicating formation takes the form of a notch or relief provided on the lower end of the delivery tube.
The present invention preferably utilizes the invention of the referenced Aspirator Probe Case in combination with a system for providing a controlled flow of liquid to a discharge control nozzle so that what discharges from the nozzle is an optimum controlled flow of media, carrier gas, liquid and propulsion fluid.
The invention of the referenced Canister Probe Case provides a means for utilizing aspirator probes of the type described in the referenced Aspirator Probe Case both (1) in the environment of a canister-type sand blast apparatus and (2) in the environment of a remote-reservoir-type sand blast apparatus of the type described previously (i.e., wherein a media supply hose connects a discharge control nozzle with an aspirator probe which is positioned in a remotely located media reservoir). In a canister-type sand blast apparatus, a canister containing granular media is connected by means of a relatively short supply conduit to a discharge control nozzle. In preferred practice wherein a canister-type reservoir is used, the supply conduit provides a rigid connection that supports the media canister from the body of the discharge control nozzle.